This invention arises from improvements to apparatus which we previously developed, and from the adaptation of such apparatus to incorporate these improvements. The previously-developed apparatus are the subjects of: U.S. Pat. Nos. 4,234,844, issued Nov. 18, 1980 for "Electromagnetic Noncontacting Measuring Apparatus"; 4,318,108, issued Mar. 2, 1982 for "Bidirectionally Focusing Antenna"; 4,878,059 issued Oct. 31, 1989 for "Farfield/Nearfield Transmission/Reception Antenna"; 4,947,848, issued Aug. 14, 1990 for "Dielectric-Constant Change Monitoring"; 4,949,094, issued Aug. 14, 1990 for "Nearfield/Farfield Antenna With Parasitic Array"; and 4,975,968, issued Dec. 4, 1990 for "Timed Dielectrometry Surveillance Method and Apparatus". All of these patents are owned in common with the present application, and all are incorporated herein by reference.
There are two primary kinds of contraband detectors presently in use in existing security system. One is a whole body scanner through which people pass and which detects contraband material, such as weapons. The other is a luggage scanner through which material passes for the purpose of detecting contraband, such as bombs. Most such detectors bombard a target with X rays which are safe with material, but which progressively produce damage in the human body over time, and are known to be linked in a causal way to tissue damage that may lead to cancer. Other detectors look for a magnetic anomaly. All such detectors are useful for detecting metals only. These prior art detectors are singularly discriminate in terms of material density, and are indiscriminate in terms of volume. Thus, while they can detect weapons, they cannot detect plastiques or illicit drugs, and they might false-positively indicate that a ring of keys is a weapon. Time-consuming visual screening of captured X ray images, in the case of luggage, greatly slows down security-checkpoint processing of people and their luggage.
Imaging approaches to personnel screening tend to be invasive of a person's privacy and modesty. In other words, screening systems that image the person's body penetrate the person's clothes and highlight the person's physical attributes, effectively undressing the person. Thus, while human body image-reproduction systems, such as X ray systems, may be law-enforcement-friendly, they are traveler-unfriendly to the extent that they constitute an invasion of privacy. Also, and in the case of X ray detecting, such systems constitute a known health hazard.